So-called robo-advisers were built on the promise of offering wealth management expertise to the masses. Now those startups are turning their attention to a different - and much wealthier - customer.

Betterment LLC, the largest startup in the automated financial advisory market, has said that it's adding a tool for some clients to adjust investment allocations in more granular ways. The service is limited to those with at least $100,000 (€81,000) under management by Betterment.

The product follows similar moves by two other robo-adviser startups in recent months. Ellevest, a women-focused investment platform founded by Wall Street veteran Sallie Krawcheck, introduced a private wealth management service late last year for clients willing to put in more than $1m. Last month, Wealthfront added a tool to minimise investment risk for customers with $100,000 or more.

Services geared toward wealthy clients typically carry larger fees, which is appealing to a young company in search of profits.

But there are doubts about whether high-net-worth individuals would be willing to move their assets to robots at an untested firm. This type of customer will "always demand face-to-face advice", according to a report from analysts at Citigroup in 2016.

Robo-advisers started out by going after people with limited disposable income and little experience with investing.

These companies are able to offer wealth management tools at low fees because they rely mostly on automated software, instead of people, to deliver advice. Customers fill out a risk profile by answering questions about their age and goals to receive a customised portfolio made up of exchange-traded funds and other passive investments.

Competition has upped the urgency for these startups to add new products. Charles Schwab, Morgan Stanley and Vanguard Group have all introduced robo-advisers in recent years and have billions of assets under management already. Betterment and Wealthfront have said they each have more than $10bn in assets.

"The industry has come a long way over the past several years, but success has also attracted new competition, including large and established players across the financial services industry," said Devin Ryan, an analyst at JMP Securities LLC.

Ellevest's product for millionaires comes at a higher cost than its base service, in exchange for access to additional investment options and a personal, human financial manager. (Bloomberg)